(1) Field of the Invention
This invention relates to photopolymerizable compositions and more particularly to thermally stable compositions containing normally dimeric nitroso compounds.
(2) Description of the Prior Art
It is known that certain aromatic nitroso compounds are useful as polymerization inhibitors. For example, Hungarian Patent 150,550 (1963) describes the use of p-aminonitrosobenzene and .alpha.-nitroso-.beta.-naphthol as inhibitors for the free radical polymerization of styrene. It is also known that N-nitrosocyclohexylhydroxylamine salts serve as thermal polymerization inhibitors in the preparation of photopolymers (U.S. Pat. No. 3,625,696, 12/7/71). Similarly, the use of 4-nitrosophenol, 1,4-dinitrosobenzene, nitrosoresorcinol, p-nitrosodimethylaniline and other nitroso compounds as inhibitors for styrene and vinyl acetate polymerizations is described by Hartel, in Chimia (Aarau), 19, p. 116 (1965); and Tyudesh et al., in Kinetics and Catalysis (USSR), 6, p. 175-181 (1965). Heiart in U.S. Pat. No. 3,203,801 describes the use of N-substituted p-nitrosoanilines as sensitometric modifiers in photopolymerization systems. Unfortunately, when these nitroso compounds are used in photopolymerizable compositions, they inhibit the photopolymerization reaction as well as the thermally-induced polymerization reaction.
It is also known that aliphatic nitroso dimers can be dissociated to nitroso monomers, either thermally or by irradiation with short wavelength ultraviolet radiation (Bluhm and Weinstein, Nature, 215, p. 1478, 1967).